VNC Enables/Causes Windows Apps to Crash

Chris Gillard chris "at"
Sat, 02 Mar 2002 20:01:43 +0000


I see the same problem with some of our Delphi 5 apps running on
NT4/SP6a servers and VNC 3.3.3R9.

We have had this problem for a year or so, but have always doubted
our own Delphi work.

Literally in the last few days we had pinned it down to the use of
VNC & certain mouse movements. You have got this in more detail.

We had tried different video drivers, to no avail.

My next move is to try Tight VNC to see if it is any different.

A real shame as VNC has been a great tool for us.

If anyone else has any bright ideas ??



-- Chris Gillard, chris "at" on 02/03/2002

On Sat, 2 Mar 2002 11:30:11 -0500, Ron Struempf wrote:
>Several of my Windows apps, written in CBuilder and Delphi, crash
>WinVNC is running.  I saw the FAQ Q39, but it says "disable any
>savers" of which I have none.  I've been using Procomm Rapid Remote
>for a
>very long time to access these servers, but switched to WinVNC
>because Rapid
>Remote is the only app I've seen so far that crashes XP.
>We are running WinVNC 3.3.3 R9 in App Mode on NT 4.0 Server.
>What I've found is:
>- The app crashes in one of several mouse events (such as
>- In my debugging, it appears as though the associated
>message never appeared
>- The crash happens when the mouse cursor passes over the
>- The crash happens whether I am connected via VNC or Rapid Remote,
>probably local as well
>- I believe that the crashes continue to happen even after I close
>but apparently at a much lower
>I have also found that if I physically click on each focusable
>control on
>the app, that the crash does not occur again until the app is
>My theory is that WinVNC is absconding with some of the WM_????
>but not suppressing the CM_???? messages they generate.  Thus, when
>the app
>processes the control message (CM_???), it expects initialization to
>been performed when the Windows message (WM_???) was received.  By
>on each of the controls, I force it to do that initialization, so
>the crash
>doesn't happen.

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